CONGRATULATIONS TO BUDABELI, GRASSHOPPERS&ANT AND SANDPIG FOR CO-FTF!
Requirements
Hike to Ground Zero (GZ), take two pictures, make observations, answer questions, submit your pictures and answers to the CO. Recommended route for at least one leg of this out-and-back journey is the Ellis Trail, with parking at the Ellis Trailhead on the Crest Highway (NM 536). The Ellis trail has lots of good outcrops, although the Crest Trail does too, of course.
Introduction
The Civilian Conservation Corp (CCC) sure was industrious in the Sandias, constructing trails and building rock steps, rock walls and rock benches along them. But about 315 million years ago (Ma) something else was industrious here as well – multitudes of marine invertebrates with the ability to extract (precipitate out) calcium carbonate (calcite) from seawater in order to build their shells – constructing what would eventually become layer upon layer of limestone, the Madera limestone in particular.
Other EC’s in the Sandias/ABQ area provide some “big picture” background on the genesis of the Albuquerque Basin, uplift of the Sandia Mountains, formation of the Great Unconformity; another EC focusses on fossils in the Madera: these EC’s are relevant to the subject of this EC:
The Great Sandia Un-Conformist EarthCache (GC1YK8V).
Great Sandia Un-Conformist, down-low (GC6V0J8).
Sandia Crest Earthcache (GC3KFAF).
Orange Crush (GCA04W2).
Background
The Pennsylvanian Period of the Paleozoic Era was a time of tumultuous plate tectonic upheaval. Much of what would become North America during that time suffered plate tectonic collisions from multiple sides as the supercontinent Pangaea was being assembled. This caused the crust to buckle/crumple, which, in the area that would become New Mexico, formed uplifts and arches of dry land and intervening shallow seas. Figure 1 from Blakey and Ranney (2008) shows the paleogeography of Pangaea at a “time slice” during the Pennsylvanian, showing various land masses and seas in what would become the western U.S. Note where New Mexico sits, and how shallow seas are indicated by the light blue shades (as opposed to dark blues of deep oceans). Note also that at this time what would become New Mexico sits astride the equator (shown in red). Here more than 300 species of marine invertebrates enjoyed warm tropical waters in which to thrive.
Note that to the west there was a major plate boundary (or boundaries) between the continent and multiple island arcs that were colliding with it. Note also there were huge mountain chains to the east and south – these also represent a major plate boundary where two or more continents had already been colliding for a long time. There are even mountains rising in what would become Colorado and very northern New Mexico: these are called the “Ancestral Rocky Mountains”, but they are not related to the current Rock Mountains because these “Ancestral” ones were completely eroded away long before the current Rocky Mountains were formed (and all that is another story). The point to notice is that New Mexico and Colorado were both relatively far from the major plate boundaries being subjected to active plate tectonic collisions at the time, and yet we observe this “buckling” (or warping) of the crust this far from these boundaries.
The Madera is mapped by Connell (2008) as the “Madera Group, undivided”. What this means is that this “Group” of rocks actually consists of a few recognized individual Formations, but that they are sometimes (often, it appears to me) lumped together. The Formations also contain separate Members. The term “Madera limestone” is often used colloquially, because much of the Madera Group contains limestone, and it is indeed the prominent limestone cliffs that are so recognizable. If this hierarchy of nomenclature sounds confusing, it is in part owing to a very complicated history of names used in academia for different Formations and Members within the Madera Group for different mountain ranges and other areas of Madera Outcrop in New Mexico. With time geologists have honed in on an accepted, more uniform system of names to use. I have been unable to find much literature specific to the Madera within the Sandia Mountains, and have not been able to find any maps of the Sandias where the Madera is segregated into the different Formations, at least, not to mention Members.
One of the best, fairly succinct descriptions of the Madera Group that I have found is actually from Wikipedia, where it helps to simplify the nomenclature as well as descriptions. Figure 2 helps to show the nomenclature hierarchy.
The Madera Group is split into the lower Gray Mesa Formation and the upper Atrasado Formation. Based on my reading and reasoning based on the known thicknesses of these formations and the height of the cliffs at the EC, I think we need to consider only the lower Gray Mesa Formation. Generally, the Gray Mesa Formation is characterized by more massive and thicker cliff-forming limestone compared to the Atrasado Formation.
The Gray Mesa Formation is, in turn, divided into the Elephant Butte Member, the Whisky Canyon Member, and the Garcia Member. Again, based on my reading and reasoning, I think we need consider only the Elephant Butte and Whisky Canyon Members for purposes of this EC. (Note: the Whisky Canyon Member is not related to Whisky Ridge in the Sandias (on which Tower 2 sits), because that’s all granite!)
Elephant Bute Member = Limestone + minor Chert over half of it + thin Shale beds.
Whiskey Canyon Member = Very Cherty Limestone + Shale beds.
The Garcia Member starts to contain more sandstone and conglomerate, and the Atrasado Formation above that starts to contain even more slope-forming conglomerates, sandstone and shale beds.
You can see conglomerates and sandstones at some cliff overlooks and along many trails going through the Madera Group in the Sandias, and these may be parts of the Madera that have been eroded away in the area of this EC. You should also see some conglomerates/sandstones on your journey to get this EC, too, if you are observant (and some pictures mentioned later will show you what to look for).
The Madera limestone is highly fossiliferous, although in the Sandias most of the fossils are microscopic, and those that are visible tend to be quite small and consist of broken up pieces. The origin of all the limestone is essentially the tiny shells and shell fragments that would remain after death and decay of the organic parts of the original invertebrates living in the shallow seas. Some calcite (calcium carbonate) can also precipitate out of solution in the seawater. With time, layer upon layer of shells, shell fragments and precipitated calcite would sink to the bottom of the seas, accumulate there in layer upon layer, compress and lithify to eventually form the limestone rock.
In truth, sea levels were rising and falling abruptly and repeatedly throughout the Pennsylvanian, so Figure 1 really shows only a “snapshot” during this Period. To drive this point home, Figure 3, also from Blakey and Ranney (2008), shows six paleogeographic maps during different times in the Pennsylvanian. Note that these pictures were obtained by me by scanning figures in a paper book, and then cropping, resizing and assembling them together; I’ve drawn some of the state borders and also the borders for Bernalillo County and a few others: these drawings are only approximate, but allow you to roughly place yourself. Note that in these figures the orientation is such that present day North is Up (unlike in Figure 1).
So, for example, Figure 3 shows that Bernalillo and adjacent counties were all land during the Early Pennsylvanian, about 316 million years ago (Ma). In fact, much of New Mexico was land, although there were some shallow seas to the south. By ~312 Ma a shallow sea stretched from north to south, going through Bernalillo County. By the Middle Pennsylvantian ~308 Ma sea levels became shallower, and then increased in depth again by ~304 Ma. In fact, there were many more oscillations in sea level than are captured here – up to about 60 – but by Late Pennsylvanian ~300 Ma the seas were shrinking again and by Permian (not shown) they had dried up completely in Bernalillo and adjacent counties.
These sea level fluctuations have been linked to glaciation patterns in the southern hemisphere at the time: sea levels rose when glaciers melted, and sea levels fell when glaciers grew in size. When sea levels were high, in New Mexico that meant that these inland seas were actually still relatively “shallow” compared to the truly deep oceans, and were hospitable to marine life: during these times marine life flourished. When sea levels were low that meant that rivers and streams on land could transport more sand, silt and shale-sized particles (clastics) further out into the seas: this influx of clastic sediments essentially “muddied” the otherwise clear tropical waters and suppressed marine invertebrate populations. (Think of the beautiful white beaches and clear waters offshore Florida, compared to the tan beaches and browner waters offshore western Louisiana and eastern Texas – down current from the silty and muddy Mississippi River Delta outflow). As a result, the formation of calcium carbonate and hence limestone decreased; deposition of limestone would be limited to the more central parts of the shallow seas farthest from the influx of “mud”. In summary, glacial periods waxed and waned repeatedly, causing sea levels to fall and rise in response, resulting in cyclic layering patterns between more clastic (shaly) layers and more calcium carbonate-rich (limestone) layers.
Let’s “fast forward” to a more recent time during and after the formation of the Albuquerque Basin and relative uplift of the Sandia Mountains. Now the Madera rocks on the upthrown sides of the basin-bounding faults have been exposed at the surface, exposed to wind, rain and running water, resulting in erosion. How rocks weather and erode is very much a function of how “hard” they are. Generally, in the relatively arid American west, limestones tend to resist erosion and tend to form pronounced cliffs and ledges; conversely shales, or rocks that are at least shaly (“muddy”), tend to erode more easily and tend to form slopes. Hence, overall cliff faces that contain alternating layers of rock types will often consist of alternating steep cliffs/ledges and gentler slopes.
Hike to Ground Zero
On your hike to GZ, if you follow the Ellis trail, you will be hiking on Madera Group rocks all the way, and there are some good outcrops and abundant good fossils. The Survey and 10K trails are more forested and generally have fewer outcrops. The Crest Trail certainly has lots of Madera outcrops. Make observations to see fossils in exposed rocks. Take one picture close up of fossils in rocks, either on your hike out to GZ, at GZ or on your way back from GZ. Be sure to include something unique to indicate scale and a general description of where you took your picture (for example, “on the Ellis Trail, between the 10K junction and the Osha Loop junction”).
Figures 4A-4D show examples of a closeup pictures of limestone with fossils taken along different stretches on the Ellis and Crest Trails. A Sharpie pen has been used in most pictures to show scale.
Figure 5 shows examples of sandstones or fine-grained conglomerates that can be found on both the Ellis and Crest trails. These are good indicators of clastic-type sediments being transported from surrounding uplands out into the sea, where they would interfere with the livelihoods of some of the shell-forming marine critters. See if you can notice this type of rock: there are several locations of outcrops along the Ellis, and one really good one on the Crest (should you go back that way; see the figure).
The descriptions of the Madera limestone from many sources describe the presence of chert, sometimes very abundant chert. The chert here can take on many colors, including almost-white, cream pale yellowish, tan, and even somewhat orange-y if stained with iron oxide. Figure 6 shows some pictures of chert nodules embedded in the limestone. The origin of chert is another story.
At Ground Zero
At GZ there are some “artifacts”. Take one picture that includes one of the artifacts and something else of yours that is unique to prove you have arrived. Do not include this picture in your log/posting, but rather send it to me via text or email. Also, do not include in your log/posting of the view to the north (described next).
At GZ there is a view looking due north of a northern promontory (or buttress) and limestone cliffs, with gray Madera Group rocks on top and tan/pinkish Sandia Granite toward the bottom, with a vegetated slope/hillside in between. Figure 7 shows a line drawing/sketch to help you identify which formation is which. The base of the Madera is generally recognized as the base of the lowest steep cliff. Between the base of the Madera and top of the Sandia Granite is the Sandia Formation, which contains conglomerates and sandstones, and at least at this location is a definite slope-former. The exact contact is hard to see (especially from this distance) owing to vegetation and rock debris that has tumbled downslope. There are many routes down through the limestones, for example to get out to the Saddle at the Needle: if you take that route you will encounter the Sandia Formation sandstone as you leave the lowest relatively steep limestone cliff: reaching the relatively gentle slope of the Sandia Formation is a relief(!).
Observe the Madera to see how many major cliffs/ledges there are and how many intervening slopes there are. Figure 8 shows an example of how this can be done for a completely different location along the western Crest. This picture was taken looking north along the uppermost La Luz Trail, between the Tram terminal terminus and the Crest Spur Trail junction. I’ve drawn white lines to crudely identify the boundaries between relatively steep cliffs/ledges and gentler slopes, and have labeled them. It’s possible to be more detailed, perhaps, but for now this is just an example.
So, again, observe the Madera in the major cliff face to the north from GZ to see how many cliffs/ledges there are and how many intervening slopes there are.
Observe which type of layer – cliff/ledge-forming or slope-forming – is the most dominant. In other words, think about whether the overall Madera Group exposed along the western facing Crest here is composed mostly of cliffs/ledges or slopes. Based on our understanding of the Madera Group, we can interpret that the steeper cliffs/ledges are probably “cleaner”-type limestones overall, while the gentler slopes are probably shalier limestones if not shales.
Questions
Q: How many “artifacts” are present at GZ? Who made them? What are they made of? (Be sure to submit a picture).
Q: Did you find any fossils along your hike to and from GZ and/or at GZ? (Be sure to submit a picture).
Q: How many major cliff/ledge-forming layers and how many slope-forming layers do you observe in the Madera? Your answer will depend in part on how you choose to “interpret” what you see.
Q: Which type of layer in the Madera Group here is the dominant type – cliff/ledge-forming or slope-forming?
Q: How would you interpret which type of environment at this particular location tended to prevail during deposition of the Madera Group sediments – an environment when glaciers had receded and sea levels had risen, or an environment when glaciers had grown and sea levels had fallen (all in a relative sense)?
Q: Can you think of another explanation for the pattern of alternating cliff/ledge-forming and slope-forming layers?
Permission
Permission for placement of this Earth Cache was obtained from District Ranger Crystal Powell with the Cibola National Forest and National Grasslands, Sandia Ranger District, Tijeras, NM, (505) 281-3304.
References
Bauer, P. W.., R. P. Lozinsky, C. J. Condie and L. G. Price, 2003, Albuquerque – A Guide to Its Geology and Culture, New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico.
Brandes, N., 2021, New Mexico Rocks!, Mountain Press Publishing Company, Missoula, Montana.
Blakely, R. C. and W. D. Ranney, 2017, Ancient Landscapes of Western North America, A Geologic History with Paleogeographic Maps, Springer.
Blakely, R. C. and W. D. Ranney, 2008, Ancient Landscapes of the Colorado Plateau, Grand Canyon Association, Grand Canyon, Arizona.
Connell, S. D., 2008, Geologic map of the Albuquerque – Rio Rancho metropolitan area and vicinity, Bernalillo and Sandoval counties, New Mexico, New Mexico Bureau of Geology and Mineral Resources.
Julyan, R. and M. Stuever, eds., 2005, Field Guide to the Sandia Mountains, University of New Mexico Press, Albuquerque.
Kelley, V. C., and S. A. Northrop, 1975, Geology of Sandia Mountains and Vicinity, New Mexico, Memoir 29, New Mexico Bureau of Mines and Mineral Resources.
Kues, B. S., 2001, The Pennsylvanian system in New Mexico – overview with suggestions for revision of stratigraphic nomenclature, New Mexico Geology, V. 23, n. 4, pp. 103-122.
Price, L. G., editor, 2010, The Geology of Northern new Mexico’s Parks, Monuments, and Public Lands, New Mexico Bureau of Geology and Mineral Resources, Socorro, New Mexico.
Wikipedia